Recently, magneto-optical memory devices such as magneto-optical disks have received much attention as memory devices having great densities and large capacities that are capable of rewriting information. For use in computers, large-capacity magneto-optical disks of 5-inch type and 3.5-inch type have already been put on the market.
In these first-generation magneto-optical disks, upon rewriting data, new data is recorded after the previous data has been erased. For this reason, it is necessary to invert the direction of an externally applied auxiliary magnetic field depending on the recording operation and erasing operation.
Among the magneto-optical memory devices, those which are capable of light-modulation overwriting have been demanded year after year because they make it possible to rewrite information without erasing former information, to enable double-sided recording, and to be easily adapted for use in multi-beam operation.
Here, in Jpn. J. Appl. Phys., Vol. 26(1987) Suppl. p. 155-159, a magneto-optical memory device capable of light-modulation overwriting, which has a recording layer and an auxiliary layer that are constituted of perpendicularly polarized magnetic films, has been introduced. In the case of rewriting data, after aligning the magnetization of the auxiliary layer to one direction by using a magnet for initialization use, a light beam whose intensity is modulated according to the data is projected while an auxiliary magnetic field is being applied from a magnet for recording use.
In this conventional arrangement, however, since a large, magnetic-field intensity ranging from 400 to 500 kA/m is required for the initialization, a large magnet has to be prepared for the initialization; this results in an adverse effect on making the magneto-optical disk apparatus more compact and thinner.